Air-break circuit breaker



Feb. 4, 1958 R. WEGMANN 2,822,448

AIR-BREAK CIRCUIT BREAKER Filed Dec. 16, 1954 5a nEs//v F164- RESIN co/vTA//v/NG SELF HARDEN/NG RESIN INVENTOR l 00A/'PSE RUT/LE ATTORNEYS ROBERT wfsMa/v/g` United States Patent Office AIR-BREAK CIRCUIT BREAKER Robert Wegmann, Wettingen, Switzerland, assignor to Aktiengesellschaft Brown, Boveri & Cie, Baden, Switzerland, a joint-stock company Application December 16, 1954, Serial No. 475,697

Claims priority, application Switzerland December 18, 1953 2 Claims. (Cl. 200-144) This invention relates to air-break circuit breakers with arc-suppressing chambers and more particularly to the composition of the walls of the arc-suppressing chamber.

It is known to employ synthetic resins having a quartz powder or glass liber filling as the walls of arc-suppressing chambers in duid-containing circuit breakers but such materials are destroyed relatively quickly when used as the walls of arc-suppressing chambers in air-break circuit breakers. Experience has shown that walls consisting mainly of organic substances can not sustain the high arc temperatures.

An object of the invention is to provide air-break circuit breakers, particularly automatic circuit breakers having a blast coil, with arc-suppressing chambers having walls formed of a hardenable resin containing a refractory oxide which protects the resin against destruction by the arc temperature. More speciiically, an object is to provide a circuit breaker of the type stated in which the resin walls of the arc-suppressing chamber are lled with rutile in an amount, by weight, which is a multiple of the resin content of the wall.

These and other objects and the advantages of the nvention will be apparent from the following specication when taken with the accompanying drawing in which:

Fig. 1 is a longitudinal section through a circuit breaker embodying the invention;

Fig. 2 is a transverse section on line 2 2 of Fig. 1;

Fig. 3 is a schematic diagram illustrative of a process for forming a wall of the arc-suppressing chamber; and

Fig. 4 is an edge elevation of another form of wall for the arc-suppressing chamber.

In Fig. 1, the reference numerals 1, 2 identify the contacts of an air-break circuit breaker which are separated by automatically operating mechanism of any known type in the event of an overload or a fault on the line. The contacts open adjacent the mouth of an arc-suppressing chamber 3 into which the arc is deected by a coil 4 in the usual manner.

The chamber 3 may be of any known form and usually will have an open top covered by a screen 3' but, in accordance with the invention, the arc-contacted surfaces of the chamber walls are provided by a layer 5 of a casting or self-hardening resin, for example a low-pressure casting resin of ethoxylin type such as that known as Araldit, with a iilling of rutile, Ti02, in a proportion by weight of about 6:1 of the resin. This relatively large proportion of inorganic filler prevents the combustion of the resin even in the case of a formation of soot on the walls of the arc-suppressing chamber.

It is preferable to employ several grain sizes of the filling compound in forming the wall material. One con- 2,822,448 Patented F eb. 4, 1958 mold 6 of the desired wall shape with coarse rutile fragments 7 of varying size and then to ll the interstices with a mixture of hardenable plastic and powdered rutile.

The walls of the arc-suppressing chamber need not necessarily consist entirely of a hardenable plastic with a rutile tilling as it is possible to build up the wall material by rst forming a relatively thin layer of rutile filled resin and then to cast on at least one additional layer 5a consisting of a hardenable resin and some other iilling material, for example quartz powder, SiO2, until the desired wall thickness is attained. Other filling materials such as aluminum oxide, A1203, or magnesia, MgO, may be employed in such additional layers. Such multilayer walls have the great advantage that the layer of resin and rutile which is contacted by the arc has favorable dielectric and thermal characteristics while the additional layer or layers have a much greater mechanical stability and electric breakdown resistance than the iirst layer.

As shown in Fig. 4, multi-layer plates for the manufacture of rectangular arc-suppressing chambers may be built up with a layer 5 containing rutile and a superposed layer 5a comprising a resin with a iilling of silica, aluminum oxide or magnesia.

The arc-blasting coil 4 and its leads can easily be incorporated in the walls of the arc-suppressing chamber, Yreferably in the outer layer 5a comprising the resin and powdered quartz or the like when a multi-layer wall is employed. The metal strips 8 which are usually incorporated in arc-suppressing chambers may, if desired, be supported by embedding edges thereof in the inner resin-rutile layer.

I claim:

l. A sparking chamber for electrical switches of the air-break circuit breaker type having blast coils, the walls of said chamber being of a multi-layer construction comprising an inner layer consisting of coarse lumps of rutile and a mixture of self-hardening resin of the ethoxylin type and powdered rutile lling the interstices between said lumps of rutile, and a second layer cast upon said iirst layer, said second layer consisting of a selfhardening resin of the ethoxylin type and a refractory oxide iiller selected from the group consisting of aluminum oxide, quartz and magnesia.

2. A sparking chamber as dened in claim 1 wherein the proportion of iilling material by weight to the resin in said inner wall is approximately 6:1.

References Cited in the le of this patent UNITED STATES PATENTS (Addition to French No. 981,678, I an. 11, 1949) OTHER REFERENCES British Plastics publication, November 1948 (pages venient method, as illustrated in Fig. 3. is to ll a hollow 55 521-523). 

